Control instrument



March 4, 1930. R. HOFSTETTER 1,748,983 I CONTROL INSTRUMENT Filed April13. 1927 Patented Mar. 4, 1930 UNITED sTArss PATENT OFFICE ROBERTHOFSTETTER, OF IDOWNERS GROVE "ILLINOIS, ASSIGNOR TO WESTERN ELEC- TRIOCOMPANY, INCORPORATED, OF NEW YORK, N. 55., A CORPORATION OF NEW YORKCONTROL ENSTRUMENT Application filed April 13, 1927. Serial No. 183,336.

This invention relates to control systems, and more particularly tocircuit controlling mechanisms for temperature control systems.

The principal object of the invention is to provide an improved,reliable and efiicient circuit controlling mechanism for controlsystems.

In accordance with the general features of the invention, there isprovided in one embodiment thereof a system for controlling thetemperature within electrically heated furnaces wherein a mechanicallyoperated fluid contact switch controlled'by a temperature measuring orindicating instrument serves to control the supply of heating current tothe furnace in response to predetermined temperature variations withinthe furnace. The measuring or indicating instrument is controlled by atemperature responsive device mounted within the furnace.

Other features and advantages of the invention will become apparent inthe following detailed description reference being had to theaccompanying drawing, wherein Fig. 1 illustrates diagrammatically atemperature control systemembodying the features of the presentinvention;

Fig. 2 is an elevational view of the mechanism for operating the mercuryswitch which controls the supply of heating current to the furnace, and

Fig. 3 is a of Fig. 2.

It is believed that the invention will be clearly understood from thefollowing detailed description of a specific embodiment thereof. Itshould be understood, however, that the invention is not to be limitedto the specific structure disclosed except as defined in the appendedclaims.

Referring now to the drawing and particularly to Fig. 1 thereof, thereference numeral 10 indicates an electrically heated furnace which maybe of any desired coiistruclion. For the purpose of clearly illustratingthe invention, the furnace as shown diagrammatically in the drawing maycomprise a cylindrical. outer casing 11 wit which a detail section takenon line 3-3 min smaller cylindrical inner casing is concentricallysupported. Encircling the inner casing 12 is an electric heating element13. Connected in series with the heating element 13 1s a fluid contactswitch 1 1 of any well known type comprising a sealed tube 15 housing apair of electrodes or contact members 16 and 17 and a body of mercury orother suitable conducting fluid 18. lhe electrodes 16 and 17 are spacedfrom each other and are adapted to be bridged by the conducting fluid toclose an electrical circuit which supplies heating current to theheating element 13. As shown in the drawing, the electrode 16 isconnected to one end of the heating element 18 by a conductor 19 and theopposite end of the heating element is connected to a conductor 20. Theelectrode 17 is connected to a conductor 21 and the conductors 20 and 21are connected through a switch 22 to any suitable source ofelectricalenergy (not shown).

The contact switch 14 is supported in a substantially horizontalposition and is mounted so that it may be tilted in either direction to.allow the conducting fluid 18 to flowinto and out of circuit makingposition to start or discontinue the supply of heating current to theheating element and means is provided for mechanically tilting thecontact switch in response to predetermined temperature variationswithin the furnace. The

tube 15'of the contact switch is supported within a spring clamp 24(Fig. 3) secured to the face of a pinion 25 rotatably journaled in avertical plate 26. The plate 26 is slidably mounted in parallel guides27 and 28 secured to a vertical supporting plate 30, which latter plateis in turn supported by suitable framework, a portion of which isindicated at 31 (Figs. 1 and 2). Secured to the plate 26 are a pair ofvertically disposed parallel guide members 33 and 34 within whichoppositely disposed racks and 36, respectively, are slidably mounted andarranged to engage opposite sides of the pinion 25. From theconstruction just described, is obvious that a reciprocatory movement isimparted to the racks 35 and 36 by the reciprocation of the plate 26 andthe pinion which is movable therewith.

A reciprocatory movement is imparted to the plate 26 by a continuouslyrotating can 38 secured to a shaft 39 which may be driven from anysuitable source of power (not shown). The cam 38 engages one end of alever 40 which is pivoted intermediate its ends upon a pin 41 carriedupon the end of an arm 42 secured to the frame 31. The opposite end ofthe lever 40 engages an arm 44 secured to the plate 26. A block securedto the supporting plate 30 is provided on its lower edge with arectangular slot 46 within which transverse portions 47 and 48 of theracks 35 and 36, respectively, are designed to enter upon the racksreaching the end of their upward movement. The block 45 is provided withelongated mounting slots 49-49 whereby its position with respect to theracks 35 and 36 may be readily adjusted.

The means for tilting the contact switch 14 to start or discontinue thesupply of heat ing current to the heating element 13 in response topredetermined temperature variations within the furnace 10 will now bede scribed. Arranged so as to be free to travel along the lower edge ofthe block 45 is a pointer 50 of a measuring or indicating in strument,such as a galvanometer 51, which is connected in the usual potentiometercircuit. As shown in Fig. 1, the galvanometer 51 is connected in serieswith a temperature responsive device such as a thermo-couple 53 mountedwithin the furnace. One end of the galvanometer coil is connected to aresistance 54 by a conductor 55 and the other end of the galvanometercoil is connected to one terminal of the thermo-couple 53 by a conductor57. The other end of the thermocouple is connected by means of aconductor 58 to a movable contact 60 which bears upon the resistance 54.The resistance 54 is connected in series with an adjustable resistance61 and a battery or source of direct current 62.

Associated with the movable contact 60 is a pointer 64 which cooperateswith a suitably calibrated scale 65 associated with the resistance 54 toindicate the temperature desired within the furnace. The resistance 61is adjusted in the usual manner so that the galvanometer pointer is inbalanced or neutral osition when the temperature indicated by t epointer 64 upon the scale 65 is equal to the temperature within thefurnace.

In the operation of the above described control system, the contact 60is adjusted according to the temperature which it is desired to maintainwithin the furnace, the temperature being indicated by the pointer 64upon the scale 65, as hereinbefore described. The switch 22 is thenclosed and assuming that upon starting the operation of the system thecontact switch 14. is tilted in the position shown in the drawing. it isobvious that electrical current is supplied to the heating element 13which supplies heat to the furnace Until the desired temperature asindicated by the pointer 64 is attained within the fur nace, thegalvanometer pointer 50 will remain deflected to the right from itsbalanced position as shown in Fig. 1. lVhen in this position, thepointer 50 serves as a stop which limits the upward movement of the rack36, whereb the contact switch is maintained tilted in tie closedposition as shown. As the temperature within the furnace approaches thedesired predetermined value, the pointer 50 moves toward the left (Fig.2) to its balanced or neutral position, and when in this position, thegalvanometer pointer is positioned in the space provided thereforbetween the adjacent ends of the transverse portions 47 and 48 of theracks 35 and 36, respectively. lVhen the temperature within the furnaceincreases above the desired predetermined value, the pointer 50 isdeflected to the left beyond the balanced or neutral position, andduring the next upward movement of the plate 26, the galvanometerpointer serves as a stop to limit the upward movement of the rack 35while the rack 36 continues to move upwardly, thereby causing thecontact switch to become tilted in the opposite direction whereby theconducting fluid 18 is disengaged from the electrodes 16 and 17, thusdiscontinuing the supply of heating current to the heating element 13.This condition prevails until the temperature within the furnaceincreases below the predetermined value, whereupon the galvanometerpointer 50 moves to the position shown in Fig. 2, thereby tilting thecontact switch into its closed position in the manner hereinbeforedescribed.

Although the invention as herein illustrated and described isparticularly applicable to systems for controlling the temperature ofelectrically heated apparatus, it should be understood that the novelfeatures of the invention are capable of other applications within thescope of the appended claims \Vhat is claimed is:

1. In an electrical control system, a circuit controlling mechanismcomprising a reciprocable member, a fluid contact switch pivotallycarried thereby, a pinion secured to said contact switch, a reciprocablerack operatively engaging the pinion, and means for reciprocating themember to cause a reciprocatory movement of the rack.

2. In an electrical control system, a circuit controlling mechanismcomprising a reciprocable member, a pinion pivotally carried thereby, afluid contact switch carried by the pinion, a reciprocable rackoperatively engaging the pinion, meanstor reciprocating the member tocause a reciprocatory movement of the rack, and a movable memberactuated in response to predetermined conditions of the system forlimiting the movement of the rack to cause a rotary movement of thepinion.

3. In an electrical temperature control system, a circuit controllingmechanism comprising a reciprocable member, a pinion pivotally carriedthereby, a fluid contact switch I carried by the pinion, a air ofoppositely dis= carried by the rotatable member and rotatable therewith,and means forrotating the rotatable member to cause a rotary movement ofthe contact switch.

In witness whereof, I hereunto subscribe my name this 15 day of March,A. D. 1921 ROBERT HOFSTETTER,

